1. Field of the Invention
This invention relates to a combination of two electrochemical techniques into a multi-effects method for pre-treating miscellaneous wastewaters. More specifically, the invention relates to electrocoagulation (EC) and electrolytic ozone (EO3) working simultaneously for quick abatement of the major pollution indices including COD, coloration, TSS, TOC, heavy metals, microorganisms and TDS of the treated waters without using chemicals and/or microbes.
2. Background of the Related Art
Water is vital to the survival of all life on the earth. Regardless of the water sources, water often requires some form of purification before use. Purification of water, or water treatment, is determined by the goals of end-use, such as, irrigation, aquatic cultivation, industrial production, or human consumption. Water can always be treated to the desired level of purity but, at a cost. When deciding a water-treatment protocol, one needs to consider the following factors: capital cost, power consumption, maintenance, throughput, foot-print area, secondary pollution, as well as post-treatment cost. Practically, capital cost and energy consumption are two most essential factors.
Seawater covers about 71% of the earth's surface, and it is the most abundant source of water. When water becomes scarce, people frequently look to the sea or ocean for water. Nevertheless, seawater is a complex waste water with average salinity of about 30 to 38 parts per thousand (ppt), or 30,000 to 38,000 parts per million (ppm), or 3.0 to 3.8%. The salinity of water is also referred as total dissolved solids (TDS) which is associated with water conductivity. In the 10 principal inorganic salts of seawater, the leading 2 ions are Cl− (55.04%) and Na+ (30.61%), followed by SO42−, Mg2+, Ca2+, K+, HCO3−, Br−, BO33− and Sr2+ to constitute 99% of the seawater salinity collectively. Besides the normal organic matter (NOM), seawater contains other organic materials depending on the estuary where seawater is taken for desalination. Distillation and reverse osmosis (RO) are the two most popular techniques for desalination around the world. For protecting boilers, heat exchangers and RO membranes from fouling by the inorganic salts and organic matters in seawater, various antiscalants or scale inhibitors, inorganic acids/bases, coagulants/precipitation agents and oxidants are employed for pre-treating the seawater as taught in U.S. Pat. No. 4,713,195; U.S. Pat. No. 7,862,727; and U.S. Pat. No. 7,931,809, as well as in Ning et al., Desalination and Water Treatment, Volume 9, pp 92-95 (2009), just to name a few. Distillation and RO are energy-thirst techniques, while distillation spends energy on heating seawater, RO consumes energy in the form of high pressure to extract freshwater out of seawater. In addition to power consumption, the use of chemicals and polymers in the pretreatments not only escalates the operation cost, but it also add burden to environment and post-treatments. Especially, RO expels treated water more polluted than the feed water to the sea, which causes severe damage to the ecology of discharge area.
Leather tanning is a centuries-old industry which provides materials for making shoes, furs/clothing, furniture, gloves, bags and belts. Leather is made from raw hide or skin, a byproduct of the meat industry, requiring an intensive use of water in many mechanical and chemical processing steps. For processing 850 Kg raw hide, it generally consumes 25-50 m3 of water and 150 Kg chemicals resulting in 250 Kg finished leather with 25-50 m3 waste water and 600 Kg solid wastes. Apparently, there are 150 Kg chemicals and 600 Kg solids dissolved or dispersed in the effluent needed to be removed prior to the discharge or re-use of the water. Although modern tannery fabrication techniques have significantly reduced the usage of water and metal, the tannery effluent is still a highly contaminated and hard-to-treat waste. Virtually all tannery effluents are black in color filled with fat, oil, grease (FOG), high SS (suspended solids, up to 3,000 ppm), high sulfide (strong foul smell), high COD (chemical oxygen demands, up to 50,000 ppm), high TKN (total Kjeldahl Nitrogen) and high TDS (up to 90 ppt). The pretreatment of tannery effluent includes flotation of FOG by dissolved air for skimming, and oxidation of sulfides by liming and aeration as taught in U.S. Pat. No. 4,913,826; U.S. Pat. No. 5,472,619, U.S. Pat. No. 6,649,067 and U.S. Pat. No. 7,670,493. In the pretreatment, a huge amount of power is spent on driving pumps, blowers, mixers and dryers (dehydrators). Furthermore, the process employs several large pools for outdoor exposure and flotation, which is space demanding and lack of sanitation. In the following primary and secondary treatments of tannery effluent, precipitation agents, coagulants and bacteria are extensively applied resulting in secondary pollution and high cost for handling the sludge produced.
Seawater and tannery effluent serve as two stubborn liquids for proving the principle and performance of the combinatory technique, EC+EO3, as a viable pretreatment method for remedying waste waters. The instant invention will present data on treating seawater and a tannery effluent by EC+EO3 using only electricity. As no chemical or microbe is involved in the treatments, the sludge formed in treating each of the said waste waters is a useful resource, an added value to the treatments by EC+EO3. The EC+EO3 treatment is also fast, energy effective and pollution free.